It is desirable for engine manufacturers to have a means for determining engine oil consumption quickly, accurately and automatically. Studies have shown that consumers consider the need to add oil to an engine between oil changes is representative of problems with engine design or performance. In addition, high oil consumption has been correlated with premature aging of catalytic converters and exhaust gas oxygen sensors, as well as high levels of hydrocarbons in the exhaust gas.
U.S. Pat. No. 5,129,257 to Carduner et al. discloses a method for determining engine oil consumption on a real-time basis. A control circuit operates to maintain a small, constant concentration of a selected electrolyte constituent reactive with the exhaust constituent sought to be measured. The amount of current necessary to regenerate and maintain the concentration of the selected electrolyte constituent is continuously measured to generate a real-time electrical signal proportional to the mass flow of the exhaust constituent entering the electrochemical cell. If the exhaust contains less than 2500 ppm of nitric oxide (NO), potassium nitrite in the electrolyte will overcome nitrogen dioxide (NO.sub.2) gas interference. However, the electrochemical cell is susceptible to NO.sub.2 gas interference in an exhaust containing more than 2500 ppm of NO due to the formation of NO.sub.2 resulting from a chemical reaction of NO and O.sub.2.
Another known method for determining engine oil consumption involves detecting SO.sub.2 utilizing ultra violet fluorescence analysis of a conditioned exhaust stream. Such a method is disclosed in U.S. Pat. No. 5,152,963 to Wreyford. A sample is first combusted to provide products of combustion, including SO.sub.2 and NO. The sample is then passed through a dryer to eliminate any water condensation. Next, the sample is directed into two different chambers: a reaction chamber for determining the nitrogen content of the sample, and a fluorescent chamber for determining the sulphur content of the sample. This system suffers from the drawback that it requires a permeation dryer which requires routine maintenance and deteriorates gradually without prior notice.
Accordingly, there exists a need for a simplified method and system for accurately and quickly determining engine oil consumption for both steady state engine operation as well as transient modes of engine operation.